1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image based on image data from an image-forming request source, and more particularly to an image forming apparatus suitable for use in a laser printer or copier which handles image data as a multiplicity of pieces of line data (dot sequences).
2. Description of Related Art
FIG. 14 of the accompanying drawings is a block diagram of a typical image forming apparatus as a common denominator of the conventional art (20xe2x80x2) and the subject invention (20) described later. The conventional image forming apparatus 20xe2x80x2, as shown in FIG. 14, generally comprises a main control section 2, an optical unit 3, a photosensitive body 4, a processing unit 5, a paper feed system 6, a low-voltage power source 7, and a high-voltage power source 8. Another element of the conventional image forming apparatus 20xe2x80x2 is a non-illustrated fixing device.
The conventional image forming apparatus 20xe2x80x2 is connected to an upper apparatus 1, such as a personal computer, a host computer or a server, for forming an object image on a sheet of paper or the like (hereinafter also called the paper or the print paper) based on an image-forming request or image data received from the upper apparatus 1.
The main control section 2 controls operations of the optical unit 3, the photosensitive body 4, the processing unit 5 and the paper feed system 6 and also sends the image data, which is received from the upper apparatus 1, to the optical unit 3 as image information.
The optical unit 3 exposes the photosensitive drum 4 to light to form an electrostatic latent image on the drum surface, including an image processing section described later.
The photosensitive body 4 is in the form of a drum or a belt whose surface is coated with a photosensitive substance (e.g., an optical photoconductor (OPC), organic semiconductor) and is exposed to laser light of LD (Laser Diode, a semiconductor laser 14 in FIG. 5) of the optical unit 3 in a pattern corresponding to image data.
The processing unit 5 applies toner to the photosensitive body 4 to develop the latent image on the photosensitive body 4, transfers the developed image from the photosensitive body to the paper, and clears residual toner off the photosensitive body 4.
The paper feed system 6 feeds the paper in the conventional image forming apparatus 20xe2x80x2. The low-voltage power source 7 supplies low-voltage power to various parts or elements, while the high-voltage power source 8 supplies high-voltage power to the photosensitive body 4 and the processing unit 5.
In the conventional image forming apparatus 20xe2x80x2, when image data together with an image-forming request is received from the upper apparatus 1, the photosensitive body 4 is exposed to light by the optical unit 3 based on the received image data, and synchronously with this exposure, feed of the paper is started by the paper feed system 6.
The processing unit 5 develops a patterned area (electrostatic latent image) on the circumferential surface (hereinafter called the surface) of the photosensitive body 4, which has a potential as exposed to light, with toner, whereupon the toner image is transferred to the surface of the paper as the paper surface is brought into contact with the surface of the photosensitive body 4.
Subsequently, the paper feed system 6 feeds the paper, onto which the toner image has been transferred, to the fixing device where the toner image is fixed to complete the forming of an object image on the paper.
FIG. 15 is a block diagram of an image processing section 9 of the conventional image forming apparatus 20xe2x80x2, illustrating the manner in which an image is formed using a single LD (1 beam mode).
The image processing section 9 includes, as shown in FIG. 15, a buffer section 10, an image quality control section 11, a data-transfer controller 12, a data-readout controller 13, and an LD 14. The image processing section 9 produces a video signal (pulse signal) to turn on/off the LD 14 based on the image data received from the upper apparatus 1 so that the LD 14 emits laser light in response to the pulse signal to expose the photosensitive body 4.
Here the image data received from the upper apparatus 1 contains a multiplicity of pieces of line data representing the object image, line data of each piece corresponding to a dot sequence of an individual line of the object image and including image information of the individual dots composing the dot sequence.
The LD 14 irradiates a laser beam on the surface of the photosensitive body 4 to form an electrostatic latent image there under the control of the image quality control section 11 in such a way that dot sequences corresponding to a plurality of pieces of line data contained in the image data are formed on the photosensitive body 4.
The image quality control section 11 extends the image data over a memory (not shown) and makes scanning using a matrix (at 100 in FIGS. 16-19). At that time the image quality control section 11 determines an actual-image-forming state of an individual dot, for every dot to be formed by the LD 14, based on the regional image information of that individual dot contained in the image data and the regional image information of other dots adjacent to that individual dot, and produces a pulse signal having a pulse width corresponding to the determined actual-image-forming state for outputting to the LD 14, thereby controlling the quality of the object image to be formed.
The buffer section 10 is disposed between the upper apparatus 1 and the image quality control section 11 for temporarily retaining the image data from the upper apparatus 1 and is composed of a predetermined number (4 in FIG. 15) of line-data buffers 10-1 through 10-4 each for storing line data of a single line of the image data received from the upper apparatus 1.
The data-transfer controller 12 stores a plurality of pieces of line data, which are contained in the image data from the upper apparatus 1. And the data-readout controller 13 reads the line data, which is stored in the line-data buffers 10-1 through 10-4 of the buffer section 10 by the data-transfer controller 12, into the image quality-control section 11.
The data store operation by the data-transfer controller 12 and the data readout operation by the data-readout controller 13 take place roughly at the same time.
FIG. 16, (a) through (c), show the line data needed when the image quality is controlled by the image quality control section 11 in the 1-beam mode.
For forming the image of a particular dot A, the image quality control section 11 determines an actual-image-forming state of the dot A based on the image information of dots of 5 (lines)xc3x977 (sequences) about the dot A, as described later in connection with FIGS. 17 through 19. Specifically, an actual-image-forming state of an individual dot on the central line is determined as the line data of 5 lines extended over a memory (not shown) of the image quality control section 11 is scanned using a matrix 100 of 5 linesxc3x977 sequences.
For making image forming in the 1-beam mode, the image data (line data) read out from the buffer section 10 by the data-readout controller 13 is inputted to the image quality control section 11 one line after another. And to determine an actual-image-forming state of each dot of line data of the 1st line partially composing the object image, as shown in (a) of FIG. 16, scanning is performed using the matrix 100 after inputting and extending the first three lines of line data L1-L3. Then, as shown in (b) of FIG. 16, an actual-image-forming state of each dot of the line data L2 is determined while the 4th line of line data L4 is inputted and extended to be scanned using the matrix 100, whereupon, as shown in (c) of FIG. 16, an actual-image-forming state of each dot of the line data L3 is determined while the 5th line of line data L5 is inputted and extended to be scanned using the matrix 100.
When necessary line data is thus extended and stored, the image quality control section 11 starts scanning using the matrix 100 and determines the actual-image-forming states of the individual dots.
As mentioned above, during the 1-beam mode, the image quality control section 11 requires line data one line after another, e.g. the line data L5 after the line data L4, to form the image of the dot A by the LD 14.
Here the scanning using the matrix 100 is performed for each line data one dot sequence to another from left to right with respect to every line of the matrix 100. With continued scanning, when a particular individual dot of each dot sequence arrives at the central position of the matrix 100, a positional relationship between the last-named dot (the central dot A) and other adjacent dots is evaluated to determine a pulse size (pulse width) for forming the image of the central dot A.
The line data to be subsequently needed for the data-readout controller 13 is sequentially inputted to the image quality control section 11 during scanning of the line data. For example, as shown in (a) of FIG. 16, the data-readout controller 13 receives the line data L4 while the image quality control section 11 performs scanning of line data around the line data L1. The foregoing procedure, i.e. scanning and determination of actual-image-forming states, is carried out for the whole image data.
FIGS. 17 through 19 illustrate how to determine an actual-image-forming state by the image quality control section 11 as the image data is scanned with respect to the matrix 100 of 5 linesxc3x977 sequences where a particular dot A is located at the central position in the matrix 100.
In FIG. 17, only the dot A is shown in the matrix 100; in the absence of any other dot adjacent to the dot, namely, if the dot A is an isolated point, the image quality control section 11 output to the LD 14 a pulse signal such as to emphasize the dot A by displaying it on a larger scale than usual.
If the dot A partially constitutes part of a horizontal line as shown in FIG. 18, the image quality control section 11 produces a pulse signal such as to thicken the whole line for emphasis and then outputs the produced pulse signal to the LD 14. And if the dot A partially constitutes part of a slanting line as shown in FIG. 19, the image quality control section 11 performs smoothing by producing a pulse signal such as to arrange auxiliary dots indicated by xe2x97xaf in FIG. 12 around the dot A so that the resulting slanting line including the dot A has step-free smooth edges, realizing an improved printed image quality.
Further, another image forming apparatus is known in which an optical unit 3 composed of a plurality of LDs for exposure.
In this multi-LD image forming apparatus, the exposure time is reduced by simultaneously exposing by a plurality of adjacently arranged LDs, thus improving the printing speed. For example, in an effort to have a desired image quality, the number of LDs to be energized is selected in accordance with a target resolution (e.g., 300 dpi or 600 dip) of the object image to be formed.
Specifically, as shown in FIGS. 14 and 20, in the conventional image forming apparatus 20xe2x80x2 whose optical unit 3 is composed of a pair of LDs 14A, 14B, exposure is performed using only one of the two LDs 14A, 14B (1-beam mode) for forming a low-resolution (e.g., 300 dpi) image, and exposure is performed using the two LDs 14A, 14B (2-beam mode) for forming a high-resolution (e.g., 600 dpi) image. Accordingly a desired image forming speed can be realized even in forming an image with high resolution, without reducing the exposure speed.
In the conventional image forming apparatus 20xe2x80x2, it is discriminated whether image forming based on the image data received from the upper apparatus 1 should be performed in the 1-beam mode or in the 2-beam mode. In determining this operation mode, the above-mentioned image resolution can be used as a criterion for discrimination.
Further, in the double-LD conventional image forming apparatus 20xe2x80x2, if the resolution (operation mode) is changed over to designate the high-resolution (2-beam mode) image forming from the upper apparatus 1 or a control panel (not shown) during the low-resolution (1-beam mode) image forming, the optical unit 3 switches the operation mode to the 2-beam mode. Otherwise if the low-resolution (1-beam mode) printing is set from the upper apparatus 1 or the non-illustrated control panel during the high-resolution (2-beam mode) image forming, then the optical unit 3 switches the operation mode to the 1-beam mode to perform exposure.
FIG. 20 is a block diagram showing an alternative image processing section 9xe2x80x2 of the conventional image forming apparatus 20xe2x80x2, illustrating the manner in which the object image is formed using the two LDs 14A, 14B (2-beam mode) The alternative image processing section 9xe2x80x2 of FIG. 20, like the previous image processing section 9, produces a video signal (pulse signal) to energize/de-energize the LDs 14A, 14B based on the image data received from the upper apparatus 1. And the image processing section 9xe2x80x2 includes, as shown in FIG. 20, in addition to the two LDs 14A, 14B, a buffer section 10A, an image quality control section 11A, a data-transfer controller 12A, and a data-readout controller 13A, which are associated with the LD 14A. Also the image processing section 9xe2x80x2 includes a buffer section 10B, an image quality control section 11B, a data-transfer controller 12B, and a data-readout controller 13B, which are associated with the LD 14B.
The two LDs 14A, 14B are disposed adjacent to each other to expose adjacent two positions on a photosensitive body 4 substantially at the same time, thereby respectively forming adjacent two dots.
The two buffers 10A, 10B temporarily retain the image data from the upper apparatus 1, each being composed of a predetermined number (4 in FIG. 20) of line-data buffers 10A-1 through 10A-4; 10B-1 through 10B-4 capable of storing line data, which are transferred from the upper apparatus 1 as image data, in units of lines.
FIG. 21, (a) and (b), illustrates how to scan image data by the image quality control sections 11A, 11B in the 2-beam mode; (a) illustrates scanning of image data by the image control section 11A, and (b) scanning of image data by the image control section 11B. Hereinafter in FIGS. 21 and 22, the dot image-formed by the LD 14A is indicated by A, and the dot image-formed by the LD 14B is indicated by B.
Also in (a) and (b) of FIG. 21, each of the matrices 100A, 100B represents a dot area of 5 lines xc3x977 sequences about a respective one of the dots A, B.
For forming an image of the dot A, the image quality control section 11A performs scanning of the matrix 100A and determines a pulse size to form the image of the dot A, using image information of the dots in the area represented by the matrix 10A.
Likewise, for forming an image of the dot B, the image quality control section 11B performs scanning of the matrix 100B and determines a pulse size to form the image of the dot B, using image information of the dots in the area represented by the matrix 100B.
FIG. 22, (a1) through (a3) and (b1) through (b3), show line data needed for the image quality control sections 11A, 11B to perform the respective image control in the 2-beam mode. (a1) through (a3) of FIG. 22 illustrates how to scan the line data extended in a memory (not shown) of the image quality control section 11A using the matrix 100A of 5 linesxc3x977 sequences. Likewise (b1) through (b3) of FIG. 22 illustrates how to scan the line data extended in a memory (not shown) of the image quality control section 11B using the matrix 100B of 5 linesxc3x977 sequences.
To the image quality control section 11A, the image data (line data) read out from the buffer section 10A by the data-readout controller 13A is inputted two lines after two lines. For example, if the first 3 lines of line data L1-L3 have already been inputted as shown in (a1) of FIG. 22, then the data-readout controller 13A inputs the next 2 lines of line data L4, L5 to the image quality control section 11A where scanning takes place with respect to the matrix 100A with the line data L3 for the center.
Likewise, to the image quality control section 11B, the image data (line data) read out from the buffer section 10B by the data-readout controller 13B is inputted two lines after two lines. In the 2-beam mode, the two LDs 14A, 14B disposed adjacent to each other output the respective beams. For example, if the first 4 lines of line data L1-L4 have already been inputted as shown in (b2) of FIG. 22, then the data-readout controller 13B inputs the next 2 lines of line data L5, L6 to the image quality control section 11B where scanning takes place with respect to the matrix 100B with the line data L4 for the center.
Accordingly, at that time, the image quality control section 11A needs the line data L4, L5 when determining an actual-image-forming state of a particular dot A, and the image quality control section 11B needs the line data L5, L6 when determining an actual-image-forming state of a particular dot B. Thus the image quality control sections 11A, 11B need three lines of line data L4-L6.
Then, as shown in (a3) of FIG. 22, the line data L6, L7 are inputted to the image quality control section 11A by the data-readout controller 13A where scanning takes place with respect to the matrix 100A with the line data L5 for the center.
Likewise, as shown in (b3) of FIG. 22, the line data L7, L8 are inputted to the image quality control section 11B by the data-readout controller 13B where scanning takes place with respect to the matrix 100B with the line data L6 for the center.
Accordingly, at that time, the image quality control section 11A needs the line data L6, L7 when determining an actual-image-forming state of a particular dot A, and the image quality control section 11B needs the line data L7, L8 when determining an actual-image-forming state of a particular dot B. Thus the image quality control sections 11A, 11B need three lines of line data L6-L8.
Subsequently, in the same manner as above, the line data is inputted to each of the two image quality control section 11A, 11B two lines after two lines by a respective one of the two data-readout controllers 13A, 13B. In the meantime, the image quality control section 11A performs scanning using the matrix 10A, and the image quality control section 11B performs scanning using the matrix 100B, thus determining the respective actual-image-forming states.
FIG. 23, (a) and (b), illustrates inputting-outputting of line data of the buffer sections 10A, 10B in the 2-beam mode according to the conventional image forming apparatus 20xe2x80x2; (a) illustrates how to input/output the line data in the buffer section 10A, and (b) , how to input/output the line data in the buffer section 10B.
In (a) and (b) of FIG. 23, on the left side of the buffer sections 10A, 10B the line data to be stored in the respective buffer sections 10A, 10B by the corresponding data-transfer controllers 12A, 12B are depicted. On the right side of the buffer sections 10A, 10B the line data to be read out from the respective buffer sections 10A,10B by the corresponding data-readout controllers 13A, 13B and to be inputted to the associated image quality control sections 11A, 11B are depicted.
As shown in (a) of FIG. 23, in the buffer section 10A, with the line data L1-L3 inputted to the image quality control section 11A, the data-readout controller 13A reads but the line data L4, L5 and transmits the readout line data L4, L5 to the image quality control section 11A (phase A1).
Further, while the data-readout controller 13A reads out the line data L4, L5 from the buffer section 10A (10A-1, 10A-2), the data-transfer controller 12A transfers the line data L6, L7, out of the image data received from the upper apparatus 1, to the buffer section 10A (10A-3, 10A-4).
Then, the data-readout controller 13A reads out the line data L6, L7 from the buffer section 10A (10A-3, 10A-4) and transmits the readout line data L6, L7 to the image quality control section 11A, and in the meantime, the data-transfer controller 12A transfers the line data L8, L9, out of the image data received from the upper apparatus 1, to the buffer section 10A (10A-1, 10A-2).
In the next step, in the same manner as above, the data-readout controller 13A reads out the line data, which has been transferred to the buffer section 10A by the data-transfer controller 12A, from the buffer section 10A and transfers the readout line data to the image quality control section 11A.
Thus, in the buffer section 10A, while the line data is transferred to two line-data buffers 10A-1, 10A-2 (or 10A-3, 10A-4), of four line-data-buffers 10A-1 through 10A-4, by the data-transfer controller 12A, the line data is read out from the other two line-data buffers 10A-3, 10A-4 (or 10A-1, 10A-2) by the data-readout controller 13A. The two line-data buffers 10A-1, 10A-2 and the two line-data buffers 10A-3, 10A-4 are alternately changed over as the image data (line data) received from the upper apparatus 1 is transmitted to the image quality control section 11A.
In the buffer section 10B, as shown in (b) of FIG. 23, the same processes as in the buffer section 10A are performed by the data-transfer controller 12B and the data-readout controller 13B. And the two line-data buffers 10B-1, 10B-2 and the two line-data buffers 10B-3, 10B-4 are alternately changed over as the image data (line data) received from the upper apparatus 1 is transmitted to the image quality control section 11B.
FIG. 24 is a circuit diagram of the image processing section of the conventional image forming apparatus, showing a data-transfer controller 12xe2x80x2 and a data-read controller 13xe2x80x2 in the image processing section of the image-quality-control-free type. The image processing section of FIG. 24 performs image forming as the 1-beam mode and the 2-beam mode are alternately selected. The data-transfer controller 12xe2x80x2 is composed of switches Sw1 through Sw3; by controllably operating the individual switches Sw1 through Sw3, it is possible to control the transfer of the image data to a buffer section 10xe2x80x2.
Likewise, the data-readout controller 13xe2x80x2 is composed of switches Sw4, Sw5 as shown in FIG. 24; by controllably operating the individual switches Sw4, Sw5, it is possible to control the readout of the image data from the buffer section 10xe2x80x2 to the LDs 14A, 14B.
The buffer section 10xe2x80x2 is composed of four line-data buffers 10xe2x80x2-1 through 10xe2x80x2-4.
The operations of the data-transfer controller 12xe2x80x2 and the data-readout controller 13xe2x80x2 will now be described in connection with the image forming in the 1-beam mode using the LD 14A in the image processing section of the image-quality-control-free type. First, the data-transfer controller 12xe2x80x2 and the data-readout controller 13xe2x80x2 fix the switches Sw2, Sw3 and the switches Sw4, Sw5 to a side and b side, respectively, whereupon the data-transfer controller 12xe2x80x2 fixes the switch Sw1 to a side and stores the image data (line data) into the line-data buffer 10xe2x80x2-1 of the buffer section 10xe2x80x2 in accordance with a timing signal.
Then the data-readout controller 13xe2x80x2 switches the switch Sw4 to a side and reads out the line data from the line-data buffer 10xe2x80x2-1 to transmit the read-out line data to the LD 14A based on the timing signal.
On the other hand, during this readout of the line data, the data-transfer controller 12xe2x80x2 switches the switch Sw1 to b side and stores the next line data into the line-data buffer 10xe2x80x2-3.
This line data processing takes place until the next switching timing signal is changed over. And the above-mentioned readout of the line data from the line-data buffer 10xe2x80x2-1 into the LD 14A takes place until this switching timing signal is changed over.
Subsequently, the data-transfer controller 12xe2x80x2 switches the switch Sw1 to a side and stores the line data into the line-data buffer 10xe2x80x2-1 again. During that time, the data-readout controller 13xe2x80x2 switches the switch Sw4 to b side and reads out the line data from the line-data buffer 10xe2x80x2-3 into the LD 14A.
During operation in the 1-beam mode, using only the two line-data buffers 10xe2x80x2-1, 10xe2x80x2-3 of the buffer section 10xe2x80x2, the image processing section of the image-quality-control-free type transmits the image data (line data), which is received from the upper apparatus 1, to the LD 14.
The operations of the data-transfer controller 12xe2x80x2 and the data-readout controller 13xe2x80x2 will now be described in connection with the image forming the 2-beam mode in the image processing section of the image-quality-control-free type.
First, the data-transfer controller 12xe2x80x2 and the data-readout controller 13xe2x80x2 fix the switches Sw1, Sw2 and the switches Sw4, Sw5 to a side and b side, respectively, whereupon the data-transfer controller 12xe2x80x2 stores the image data (line data) into the line-data buffer 10xe2x80x2-1 of the buffer section 10xe2x80x2 based on a timing signal.
Then the data-transfer controller 12xe2x80x2 switches the switch Sw2 to b side with the switch Sw1 fixed to a side and stores the next line data into the line-data buffer 10xe2x80x2-2. And the data-readout controller 13xe2x80x2 switches the switches Sw4, Sw5 to a side and read out the line data from the line-data buffer 10xe2x80x2-1 to the LD 14a and also from the line-data buffer 10xe2x80x2-2 to the LD 14B in synchronism with a timing signal.
During that time, the data-transfer controller 12xe2x80x2 switches the switch Sw1 to b side with the switch Sw3 fixed to a side and stores the next line data into the line-data buffer 10xe2x80x2-3, whereupon the data-transfer controller 13xe2x80x2 switches the switch Sw3 to b side and stored the line data into the line-data buffer 10xe2x80x2-4.
Subsequently, the data-readout controller 13xe2x80x2 switches the switches Sw4, Sw5 to b side and reads out the line data from the line-data buffers 10xe2x80x2-3, 10xe2x80x2-4 to the LDs 14A, 14B, respectively.
The read-out line data in the LDs 14A, 14B is inputted directly to a driver of the LDs 14 A, 14B so that the LDs 14A, 14B are driven by the inputted line data.
FIG. 25 is a circuit diagram of the data-transfer controller and the data-readout controller in the first-named image processing section 9 of the conventional image forming apparatus 20xe2x80x2 of the image-quality-control type. The image processing section 9 of FIG. 25 also performs image forming in a selective one of the 1-beam mode and the 2-beam mode. The image processing section 9 includes a data-transfer controller 12C, buffer sections 10A, 10B, data-readout controllers 13A, 13B, image quality control sections 11A, 11B, and LDs 14A, 14B.
The data-transfer controller 12C is composed of switches Sw1 through Sw7; by controllably switching these switches, it is possible to control the transfer of image data to the buffer sections 10A, 10B (line-data buffers 10A-1 through 10A-4; 10B-1 through 10B-4).
In the meantime, the data-readout controller 13A is composed of two switches Sw8, Sw9; by controllably switching these switches, it is possible to control the readout of the image data from the line-data buffers 10A-1 through 10A-4 of the buffer section 10A to the image quality control section 11A.
Likewise the data-readout controller 13B is composed of two switches Sw10, Sw11; by controllably switching these switches, it is possible to control the readout of the image data from the line-data buffers 10B-1 through 10B-4 of the buffer section 10B to the image quality control section 11B.
FIG. 26 shows a matrix defining switching operations of the individual switches Sw1 through Sw 11 in the data-transfer controller 12C and the data-readout controllers 13A, 13B in FIG. 25. By controlling the switching operations of the individual switches Sw1 through Sw11 in accordance with this matrix, it is possible to transmit the image data, which has been received from the upper apparatus 1, successively downstream to the image quality control sections 11A, 11B.
Specifically, first the data-transfer control section 12C sets the switches Sw1, Sw2, Sw4 to a side to store the line data into the line-data buffer 10A-1 (step 1). Then the data-transfer controller 12C sets the switches Sw1, Sw2 and the switch Sw4 to a side and b side, respectively, to store the line data into the line-data buffer 10A-2 (step 2).
Subsequently, the data-transfer controller 12C sets the switches Sw1, Sw6 and the switch Sw2 to a side and b side, respectively, to store the line data into the line-data buffer 10B-1 (step 3), and also sets the switch Sw1 and the switches Sw2, Sw6 to a side and b side, respectively, to store the line data into the line-data buffer 10B-2 (step 4).
Then the data-transfer controller 12C sets the switch Sw1 and the switches Sw3, Sw5 to b side and a side, respectively, to store the line data into the line-data buffer 10A-3. And the data-readout controller 13A sets the switches Sw8, Sw9 to a side to read out the line data from the line-data buffers 10A-1, 10A-2 to the image quality control section 11A, while the data-readout controller 13B sets the switches Sw10, Sw11 to a side to read out the line data from the line-data buffers 10B-1, 10B-2 to the image quality control section 11B (step 5).
Further, in the same manner as above, the data-transfer controller 12C stores the line data into the line-data buffers 10A-4, 10B-3, 10B-4 in this order (steps 6 through 8). Then the data-readout controllers 11A, 11B switches the switches Sw8 through Sw11 to the b side to read out the line data from the line-data buffers 10A-3, 10A-4, 10B-3, 10B-4 to the image quality control sections 11A, 11B, respectively (steps 9 through 12).
The storing of the line data into the buffer section 10 in steps 9 through 12, likewise in steps 1 through 4, is carried out with respect to the line-data buffers 10A-1, 10A-2, 10B-1, 10B-2.
Subsequently, in the same manner as above, the data-transfer controller 12C and the data-readout controllers 13A, 13B controls the switching operations of the individual switches Sw1 through Sw11.
However, the foregoing conventional image forming apparatus 20xe2x80x2 would encounter the following problems. For example, in the image-quality-control-type conventional image forming apparatus 20xe2x80x2 in which image forming is possible in the 2-beam mode, since the image quality control sections 11A, 11B would need always two lines of line data for scanning a single line of line data, four line data buffers 10A-1 through 10A-4 and 10B-1 through 10B-4 would be required for the respective buffer sections 10A, 10B.
Accordingly, as mentioned above, in the image-quality-control-type conventional image forming apparatus in which image forming is possible using a plurality of LDs 14, there are required the data-transfer controller 12, the buffer section 10, the data-readout controller 13, and the image quality control section 11 for every LD 14. This necessitates total eight line-data buffers to store the line data for the whole apparatus, which would cause a complicated apparatus structure and retard a reduced manufacturing cost.
And in the other conventional image forming apparatus in which image forming is possible in a multi-beam mode using a plurality of LDs, scanning is performed using duplicating line data in the image quality control sections 11 provided one for each LD 14. In sending such duplicating line data from the upper apparatus 1 to the image control sections 11, first the data-transfer control section 12 stores the duplicating line data (e.g., the line data L7 in phase A1 depicted in (a) and (b) of FIG. 23) into the line-data buffers of the buffer section 10, whereupon the data-readout controller 13 reads out the duplicating line data, causing the repetition of the data storing process, which would be inefficient.
With the foregoing problems in view, it is an object of the present invention to provide an image forming apparatus in which possible duplicated line data can be efficiently treated to avoid wasteful transmission of such line data, minimizing the number of necessary buffers, and hence resulting in simplified construction of the apparatus and reduction of the cost of manufacture.
In order to accomplish the above object, according to the present invention, there is provided an image forming apparatus for forming an object image based on image data from an image-forming request source, the image data including a multiplicity of pieces of line data relating to the object image, each piece of line data corresponding to a dot sequence for a single line of the object image and containing regional image information of the individual dots composing the dot sequence, the apparatus comprising:
an image forming section having a plurality of dot-sequence forming units for forming a plurality of dot sequences simultaneously as one set, which sequences correspond to a plurality of pieces of line data contained in the image data and are disposed adjacent to one another, the image forming section being operative to form whole of the object image in a first mode, in which the object image is formed in units of the dot-sequence sets one set after another, repeatedly using the plurality of dot-sequence forming units;
a plurality of image quality control sections, corresponding to the respective dot-sequence forming units, for determining an actual-image-forming state of each of the dots to be formed by the corresponding dot-sequence forming unit, based on the regional image information of each of the dot and that of other dots adjacent to each of the dot, and for outputting the determined actual-image-forming state of each of the dot to the associated dot-sequence forming unit to thereby control the object image in quality;
a buffer section having a predetermined number of line-data buffers each for storing the line data of an individual line received from the image-forming request source as the image data to temporarily hold the image data from the image-forming request source between the image-forming request source and the image quality control sections, the buffer section being shared by the image quality control sections; and
a data-store-and-read control section for controlling a data store operation of storing a plurality of pieces of line data, which are contained in the image data from the image-forming request source, simultaneously into part of the predetermined number of line-data buffers, and a data readout operation of reading a plurality of pieces of line data, which are stored in the remaining part of the predetermined number of line-data buffers, simultaneously to the image quality control sections, in a way that the data store operation and the data readout operation are executed in parallel.
As a preferred feature, the predetermined number of the line-data buffers is set to a minimum necessary number to execute the data store operation and the data readout operation in accordance with both the number of the dot-sequence forming units and the number of pieces of line data needed when the image quality control sections respectively determine the actual-image-forming states of the individual dots.
As another preferred feature, the data-store-and-readout control section includes: a data-transfer controller for controlling the data-store operation; a data-readout controller for controlling the data readout operation; a store-destination switch, responsive to the data-transfer controller, for selecting part of the line-data buffers as destination buffers into which the pieces of line data are to be simultaneously stored; a readout-destination switch, responsive to the data-readout controller, for selecting part of the image quality control sections as a destination image quality control section to which the pieces of line-data simultaneously read out from the remaining line-data buffers are to be transferred to the selected part of the image quality control sections; and a switch controller for controlling the switching operations of the store-destination switch and the readout-destination switch in synchronism with the operation of the selected part of the image quality control sections.
As still another preferred feature, the image forming section has a function of forming the object image in a selected one of the first mode and a second mode in which the object image is formed stepwise one at a single dot sequence using a selected one of the dot-sequence forming units. And when the image forming unit forms the object image in the second mode, the switch controller controls the store-destination switch in a way that at least two of the line-data buffers for the second mode to which buffers the line data is to be transferred from the image-forming request source are changed from one to another in synchronism with the operation of the dot-sequence forming units in the second mode, and the switch controller controls also the readout-destination switch in a way that the dot-sequence forming units for the second mode to which unit the line data is to be transferred from the at least two of the line-data buffers in the second mode are changed from one to another.
As a further preferred feature, each of the dot-sequence forming units includes a semiconductor laser for emitting a laser beam to form each dot-sequence, which constitutes part of the object image.
With the foregoing features of the image forming apparatus of the present invention, it is possible to guarantee the following advantageous results:
(1) Partly since the single buffer section can be shared by the plural image quality control sections, and partly since the line data store operation and the line data readout operation can be executed in parallel, it is unnecessary to provide a plurality of buffer sections one for each image quality control section, causing a simplified construction of the apparatus and a reduction of the cost of manufacture. Further, the same line data would not be stored or read in duplicate, thus realizing an efficient data management.
(2) Since the predetermined number of the line-data buffers can be set to a minimum necessary number to execute the data store operation and the data readout operation, in accordance with both the number of dot-sequence forming units and the number of pieces of line data needed when the image quality control sections respectively determine the actual-image-forming states of the individual dots, it is possible to construct the buffer section with a decreased number of line-data buffers, simplifying the apparatus construction and hence reducing of the cost of manufacture.
(3) It is possible to surely execute the data store operation and the data readout operation improving the reliability of the image forming apparatus.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.